https://doi.org/10.1351/goldbook.10099
In multivariate calibration the average of the squared deviation of estimated values from the values of evaluation data. For \(N\) evaluation data where \(c_{i}\) is an observed value and \(\hat c_{i}\) is the predicted value. \[E_{\rm{MSEP}} = \frac{\sum\limits_{i\,=\,1}^{i\,=\,N} (\hat c_{i}\,-\, c_{i})^2}{N}\]
Note: Mean squared error of prediction is the square of root mean squared error of prediction.